The U’s went into the game with the best defensive record in Sky Bet League Two, but conceded three Scott Hogan goals in less than 20 minutes to lose 3-0 at fellow promotion hopefuls Rochdale.
It was the side’s biggest loss since going down 4-0 at home to Rotherham United last March.
Jake Wright and Michael Raynes both volunteered to start after missing a month with knee and hip injuries respectively.
Neither looked particularly comfortable to play 90 minutes away to a side with the best home record in the division.
Raynes, whose mis-kicked clearance gifted the third goal, conceded the challenge had come too soon for him.
But Lewis, who a week earlier handed Sam Long his first senior start and fielded Scott Davies in an unfamiliar left back role in the 1-1 draw at Morecambe, argued there were risks with whichever side he had selected.
He said: “Every time you pick a team there’s always something.
“Sometimes you gamble because you put a couple of young kids in and they do well.
“That’s the way it is, they both trained well this week and put themselves forward to play.
“They are both experienced players. Michael Raynes made a mistake for one of the goals and that just happens.”
The afternoon might have been very different had Johnny Mullins converted an excellent chance when the game was goalless.
Lewis rued the wasted opportunity, but had no complaints over the result as United had a hand in all three of Rochdale’s goals.
He said: “We could’ve gone a goal up, that might have been unfair on them.
“You try and get to half-time at 0-0 then and we just switched off at the throw-in.
“Everyone was determined in the second half to come out and try to turn it around, but we made a couple of mistakes.
“We gave the ball away and they scored on the counter-attack, which is something we had talked about in the week, because they are very good at it.”
He added: “I think it was a lack of quality in all honesty.”